Tappet for an internal combustion engine valve drive

ABSTRACT

A tappet (1) is made such that it can be coupled for different valve lifts. To assure a sufficiently rapid supply of hydraulic medium to the coupling means (10) of the tappet (1) in the base circle phase of the cam, according to the invention, the tappet (1) is in permanent hydraulic communication with a supply gallery (23). As a result of this, a pre-pressure of hydraulic medium already prevails in the reservoir (15) in front of the coupling means (10) immediately before the desired coupling, so that the desired coupling of the coupling means (10) can take place sufficiently rapidly even at high speeds of rotation of the internal combustion engine.

DESCRIPTION

1. Field of the Invention

The invention concerns a tappet for a valve train of an internalcombustion engine for a valve train, which tappet (1) is installed in abore (6) of a cylinder head (7) of an internal combustion engine and canbe switched to different valve lifts for at least one gas exchangevalve, said tappet (1) comprising an annular and a circular bottomsection (2, 3) arranged concentrically to each other and contactableeach one by a cam of different lift, the tappet (1) being guided in thebore (6) by a skirt (4) connected to the annular bottom section (2),said annular and circular bottom sections (2, 3) being dispaceablerelative to each other and adapted to be coupled to each other in theregion of their common annular plane (8) by coupling means (10) whichare displaceable radially or secant-like by a servo medium at least in afirst direction of displacement, the skirt (4) comprising at least oneinlet (25) for the servo medium, which inlet (25) serves to convey theservo medium from one end (22) of a supply gallery (23) which intersectsthe bore (6) of the cylinder head (7) to a reservoir (15) arranged in atleast one of the bottom sections (2, 3).

2. Background of the Invention

Such a tappet is known for example from EP-OS 06 20 36. A drawback ofthis tappet is that its hydraulic medium supply paths are situated inthe bore of the cylinder head. This requires complicated modificationsto cylinder heads of known design or an expensive manufacture of thesepaths in the cylinder heads. At the same time, due to their height, itis not guaranteed that the coupling means can be permanently suppliedwith hydraulic medium. Besides this, the prior an contains no suggestionfor a person skilled in the art as to how the switching operation of thecoupling means can be accelerated. Under unfavorable conditions, it ispossible, especially at high engine speeds that the available switchingtime window is not sufficient to build up the pressure required for adisplacement of the coupling means in the reservoir concerned, Since, asa rule, such coupling means are reset by mechanical spring means, it isonly the short time interval "cam base circle" that is available to thespring means to reset the coupling means with falling servo mediumpressure by pressing the servo medium back into the gallery

At the same time, according to EP-OS 06 20 360, a separate path leadingfrom the cylinder head is provided for a hydraulic medium supply to ahydraulic clearance compensation clement arranged in the tappet. Thisseparate path in the cylinder head necessitates separate oil ducts inthe tappet concerned. This likewise increases the costs of manufactureboth of the cylinder head and the tappet.

OBJECT OF THE INVENTION

It Is therefore the object of the invention to create a tappet of theinitially cited type in which the mentioned drawbacks are eliminated anda low-wear switching is permitted even at high engine speeds,particularly with the use of simple means.

SUMMARY OF THE INVENTION

The tappet of the invention for a valve train, which tappet is installedin a bore of a cylinder head of an internal combustion engine and can beswitched to different valve lifts for at least one gas exchange valve,said tappet comprising an annular and a circular bottom section arrangedconcentrically to each other and contactable each one by a cam ofdifferent lift, the tappet being guided in the bore by a skirt connectedto the annular bottom section, said annular and circular bottom sectionsbeing displaceable relative to each other and adapted to be coupled toeach other in the region of their common annular plane by coupling meanswhich are displaceable radially or secant-like by a servo medium atleast in a first direction of displacement, the skirt comprising atleast one inlet for the servo medium, which inlet serves to convey theservo medium from one end of a supply gallery which intersects the boreof the cylinder head to a reservoir arranged in at least one of thebottom sections, is characterized in that a path to the inlet is createdon or in the outer peripheral surface of the skirt, an extent of thepath is such that the path is in hydraulic communication with the end ofthe supply gallery during an entire stroke of the tappet or during asubstantial part of the stroke of the tappet.

The features create a permanent supply of the tappet described here withservo medium. At the same time, no complicated modifications to cylinderheads of known design are required because the supply paths concernedare arranged in the skirt of the switchable tappet. The servo medium ispreferably a hydraulic medium. However, air or brake fluid and the likeare also proposed as servo media and covered by the scope of protectionof the invention. Consequently, for the hydraulic displacement of thecoupling means, for example, the reservoir can be pre-pressurizedalready before the actual coupling phase, so that in the subsequent basecircle phase, this pre-pressure can be utilized for a fasterdisplacement of the coupling means. This results in a drastic reductionof the time required for building up the necessary pressure in thereservoir. A tappet which is permanently supplied with a servo medium isequally advantageous also for a mechanical resetting of the couplingmeans in opposition to the falling pressure medium pressure because theentire tappet stroke is available for the reduction of pressure. Inplace of mechanical means it is also possible to use magnetic,electromagnetic or indirectly mechanically actuated means and the like.It is equally possible to replace the servo medium with these means.

The invention applies equally to switchable tappets whose two bottomsections are coupled by spring force in the absence of servo mediumpressure and to switchable tappets in which a coupling of the twosections is achieved by coupling means pressurized by servo assistance.

The required permanent supply of pressure medium to the tappet isadvantageously achieved according to the invention by a depression suchas a bead extending in longitudinal direction on the outer peripheralsurface of the skirt of the tappet, which depression, due to a securingof the tappet against rotation, is permanently supplied with pressuremedium from one end of a supply gallery of the cylinder head.Advantageously, this depression is made in the skirt of the tappetwithout chip removal, but cutting procedures may also be used. Thedepression can comprise a cam-proximate inlet on the skirt, which inletcommunicates directly with the reservoir, but this inlet may also bearranged at a cam-remote position on the skirt, in which case, a channelleading to the reservoir extends on the inner peripheral surface of theskirt.

In an embodiment alternative to the previous one, the skirt comprises atleast one axially extending aperture which communicates with the end ofthe supply gallery of the cylinder head and comprises in its upperregion, an inlet into the reservoir of the annular bottom section.

Advantageously, the reservoir of the annular bottom section is delimitedin cam-distal direction by an annular element extending on the innerperipheral surface of the skirt and comprising a radially outer axialextension which extends on and is fixed to the inner peripheral surfaceof the skirt. Radially inwardly, the annular element can also be bent,for example, axially in a cam-distal direction and bear sealinglyagainst an axial extension of the annular bottom section.

A simple anti-rotation device for the tappet relative to its receptionbore in the cylinder head comprises, according to the invention, forexample, a cylinder such as a roller needle arranged In the skirt of theannular bottom section. However, it is also conceivable and within thescope of the invention to use bodies of any kind which project axiallyoutwards from the skirt and engage a recess of the cylinder head. Forthe same purpose, it is likewise conceivable to arrange an anti-rotationdevice locked in place in the cylinder head and extending into acomplementary longitudinal recess of the skirt.

According to the invention, the tappet is provided with a hydraulicclearance compensation element. This enables the omission of complicatedmechanical valve clearance adjusting measures during the operation ofthe internal combustion engine. In this connection, it is particularlysimple to provide a common supply from the supply gallery In thecylinder head to the coupling means and the hydraulic clearancecompensation element in the tappet. However, it is also possible toarrange separate supply ducts in the tappet starting from the cylinderhead.

Advantageously, the coupling means are configured as radiallydisplaceable pistons which extend in corresponding receptions of theannular and circular bottom sections.

According to the invention, it is further possible to retain the pistonsacting as coupling means, for example, in receptions of the circularbottom section by the force of tension springs and to displace themradially outwards for coupling into corresponding receptions of theannular bottom section by the servo medium.

Further, as already mentioned above, the method describe appropriatemethod steps for the pressurizing and pressure-relieving of thereservoir, but the scope of the invention also includes method stepswhich do not concern the entire time period stated in the claims. At thesame time, these claims also pertain to switchable tappets which aresupplied with hydraulic medium by means other than the described paths,for example, through paths in the bores of the cylinder head.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is represented in the drawings which show:

FIG. 1, a longitudinal section through a tappet of the invention in theregion of the coupling means,

FIG. 2, a tappet according to FIG. 1 but in a sectional view turnedthrough 90°, and a depression forming a hydraulic medium path on theskirt,

FIG. 3, a similar embodiment in a view corresponding to the previousone,

FIG. 4, a top view of a tappet according to FIG. 3 with partial views ofthe hydraulic medium path, and

FIG. 5, an alternative to the above-mentioned embodiments, having anaperture in the skirt forming a hydraulic medium path.

DETAILED DESCRIPTION OF THE DRAWINGS

Only such features of the tappet as are important for the description ofthe invention will be described here because a tappet of the typeconcerned is sufficiently well-known in the technical field (see, forexample, DE-OS 43 14 619).

The tappet 1 comprises an annular and a circular bottom section 2, 3.The annular bottom section 2 is loaded by at least one cam, not shown,having a large lift, and the circular bottom section 3 situated adjacentthereto is loaded by a cam having a smaller or zero lift. Radiallyoutwardly, the annular bottom section 2 comprises a thin-walled skirt 4extending in cam-distal direction. The tappet 1 extends with an outerperipheral surface 5 of the skirt 4 in a bore 6 (see also FIG. 2) of acylinder head 7. The two bottom sections 2, 3 are displaceable relativeto each other in the region of their common annular plane 8. Thecircular bottom section 3 comprises a reception 9 within which couplingmeans 10 configured as pistons extend with their entire length in theuncoupled state of the two sections 2, 3. Each coupling means 10 isretained radially inwards (further direction of displacement) by theforce of a tension spring 11. The coupling means 10 can be displacedradially outwards in a first direction of displacement by servoassistance, for example, by hydraulic medium pressure, into acomplementary reception 12 of the annular bottom section 2. In thisstate of coupling, the tappet 1 follows the lift of the cam which loadsthe annular bottom section 2, while, otherwise, the tappet 1 executesonly a stroke in response to the lift of the cam which loads thecircular bottom section 3.

A person with knowledge in the technical field will also see from FIG. 1that an anti-rotation device 13 in the form of a cylinder is fixed inthe skirt 4. This anti-rotation device 13 extends in a complementarylongitudinal groove 14 of the bore 6 of the cylinder head 7.

The sectional view of FIG. 2 additionally shows that the annular bottomsection 2 comprises an annular reservoir 15 for hydraulic medium, whichreservoir is delimited in cam-distal direction by an annular element15a. Radially inwardly of this reservoir 15, a hydraulic medium channel16 leading from the reservoir 15 to the coupling means 10 and to ahydraulic clearance compensation element 18 is formed by a guide sleeve17 which extends from the circular bottom section 3 in cam-distaldirection. This clearance compensation element 18 cooperates through itspressure piston 19 with an end of a gas exchange valve, not shown.

As shown in FIG. 2, a longitudinally extending depression 20 is arrangedon the outer peripheral surface 5 of the skirt 4 to form a path forhydraulic medium. In the base circle phase of the cam, this depression20 is in hydraulic communication through its lower end 21 with an end 22of a hydraulic medium supply gallery 23. The length of the depression 20is such that the depression 20 is in hydraulic communication with theend 22 during the entire cam lift. The depression 20, which can be made,for examples, as a bead, comprises at its upper end 24, an inlet 25 forhydraulic medium. Thus the tappet 1 is adequately supplied withhydraulic medium from the supply gallery 23 during its entire stroke.If, now, for example, a hydraulic, radially outwards displacement of thecoupling means 10 for a coupling of the two sections 2, 3 is desired, dhydraulic medium pre-pressure is built up in the reservoir 15 with acommencing run-on phase of the cam immediately before the desired pointof time of coupling. When the base circle phase of the cam in which thecoupling of the two sections 2, 3 is to be effected is reached, thispre-pressure together with the still existing full hydraulic mediumpressure is fully sufficient to displace the coupling means 10 at a highspeed into the corresponding receptions 12. It is, however, likewiseconceivable, to also provide, in a manner not specified here,longitudinal grooves in the region of the hydraulic medium channel 16,through which grooves hydraulic medium pressure can be conveyed to thecoupling means 10 already in the afore-mentioned cam lift phase.

In an analogous manner, the reservoir 15 can be relieved of pressuremedium pressure with a commencing run-on phase of the cam immediatelybefore a desired uncoupling of the two sections 2, 3, so that in thesubsequent base circle phase, because of the low hydraulic mediumpressure acting on the coupling means 10, these coupling means 10 can bepulled Into their uncoupling position by the force of their springs. Itis understood that such a permanent hydraulic supply of the reservoir 15is also possible if the required supply paths are arranged inlongitudinal grooves of the cylinder head and communicate withcorresponding transfer opening; in the skirt 4, and said permanenthydraulic supply can likewise be implemented in switchable supportelements for cam followers.

FIG. 3 shows an alternative to the preceding embodiment. The path 20 isagain made as a depression but the further transport of hydraulic mediumfrom the path 20 is realized in this case on an inner peripheral surface26 of the skirt 4. For this purpose, a radially outer extension 27 ofthe annular element 15a extends on the inner peripheral surface 26 ofthe skirt 4 in cam-distal direction. A channel 28 (see also FIG. 4)starting from the lower end 21 of the depression 20 extends between theinner peripheral surface 26 and the axial extension 27 towards thereservoir 15. As can likewise be seen in FIG. 4, this channel 28 canalso be arranged slightly offset in peripheral direction to the inlet25.

Finally, FIG. 5 shows a configuration of the path 20 as an alternativeto the already described figures. In this case, the path 20 is made asan aperture in the skirt 4. This aperture again communicates at itslower end 21 with the end 22 of the supply gallery 23. The inlet 25 intothe reservoir 15 is arranged in the region of the upper end 24. In axialdirection, the upper end 24 of tile inlet 25 is situated above theannular element 15a, The axial extension 27 again extendscircumferentially on the inner peripheral surface 26 of the skirt 4 andthus overlaps the aperture 20 radially,

We claim:
 1. A method of servo assisted displacement of the couplingmeans (10) of a tappet (1) for a valve train, which tappet (1) isinstalled in a bore (6) of a cylinder head (7) of an internal combustionengine and can be switched to different valve lifts for at least one gasexchange valve, said tappet (1) comprising an annular and a circularbottom section (2,3) arranged concentrically to each other andcontactable each one by a cam of different lift, the tappet (1) beingguided in the bore (6) by a skirt (4) connected to the annular bottomsection (2), said annular and circular bottom sections (2,3) beingdisplaceable relative to each other and adapted to be coupled to eachother in the region of their common annular plane (8) by coupling means(10) which are displaceable radially by a servo medium at least in afirst direction of displacement, the skirt (4) comprising at least oneinlet (25) for the servo medium, which inlet (25) serves to convey theservo medium from one end (22) of a supply gallery (23) which intersectsthe bore (6) of the cylinder head (7) to a reservoir (15) arranged in atleast one of the bottom sections (2,3) wherein a path (20) to the inlet(25) is created on or in the outer peripheral surface (5) of the skirt(4), an extent of the path (20) is such that the path (20) is inhydraulic communication with the end (22) of the supply gallery (23)during at least part of the stroke of the tappet (1), the method ofdisplacement of the coupling means in the first direction ofdisplacement, comprising a first step in which, prior to the firstdirection of displacement, the reservoir (15) is provided with apre-pressure of servo medium during the entire time interval between acommencing valve lifting phase of the cam and a subsequent base circlephase of the cam, and a further step in which, in the subsequent basecircle phase of the cam, the reservoir (15) is provided with the full,hydraulically required displacing pressure.
 2. The method of claim 1wherein the path (20) is formed by a depression extending essentiallylongitudinally on the outer peripheral surface (5) of the skirt (4), alower end (21) of the depression communicates with the end (22) of thesupply gallery (23) and an upper end (24) of the depression communicateswith the inlet (25) in the skirt (4), the inlet (25) opens directly intosaid reservoir (15), and the tappet (1) is guided secured againstrotation in the bore (6) in the cylinder head (7) (FIG. 2).
 3. Themethod of claim 1 wherein the reservoir (15) in the annular bottomsection (2) is delimited in a cam-distal direction by an annular element(15a) attached to an inner peripheral surface (26) of the skirt (4). 4.The method of claim 1 wherein path (20) is formed by a depressionextending generally longitudinally on the outer peripheral surface (5)of the skirt (4), a lower end (21) of the depression communicates withthe end (22) of the supply gallery (23), and the inlet (25) is arrangedin this region in the skirt (4), the reservoir (15) is delimited by anannular element (15a) attached to the inner peripheral surface (26) ofthe skirt (4), which annular element (15a) is fixed radially outwardlyon the inner peripheral surface (26) of the skirt (4) by an axialextension (27) extending in a cam-distal direction, a channel (28)starting from the inlet (25) is formed in the axial extension (27) andleads to the reservoir (15), and the tappet (1) is guided securedagainst rotation in the bore (6) of the cylinder head (7) (FIGS. 3, 4).5. The method of claim 1 wherein the path (20) is formed by an apertureextending essentially longitudinally on the outer peripheral surface (5)of the skirt (4), a lower end (21) of the aperture communicates with theend (22) of the supply gallery (23), the reservoir (15) in the annularbottom section (2) being delimited in cam-distal direction by an annularelement (15a) attached to the inner peripheral surface (26) of the skirt(4), which annular element (15a) is fixed radially outwardly against theinner peripheral surface (26) of the skirt (4) by an axial extension(27) which extends in a cam-distal direction and delimits the path (20)radially inwardly, an upper end (24) of the aperture being situatedaxially above the annular element (15a), so that the inlet (25) isformed between the two elements (15a, 24), and the tappet (1) is guidedsecured against rotation in the bore (6) of the cylinder head (7) (FIG.5).
 6. The method of claim 2 wherein an anti-rotation device (13) in theskirt (4) is formed by at least one cylinder projecting radiallyoutwards from the skirt (4) and extending in a complementarylongitudinal groove (14) of the cylinder head (7).
 7. The method ofclaim 1 wherein the circular bottom section (3) comprises on an end face(29) remote from the cam, a guide sleeve (17) comprising a hydraulicclearance compensation element (18) which cooperates with at least onegas exchange valve.
 8. The method of claim 7, wherein starting from thereservoir (15), a common supply of hydraulic medium to the couplingmeans (10) and the clearance compensation element (18) is created in thetappet (1).
 9. The method of claim 1 wherein the coupling means (10) arepistons which, in the uncoupled state of the elements (2, 3) extend in areception (9) in the circular bottom section (3) and, for coupling, canbe displaced radially outwards into a reception (12) of the annularbottom section (2) by servo medium pressure acting in opposition to atension spring force.
 10. The method of claim 2 wherein the depression(20) is made in the form of a bead.
 11. A method of displacement of thecoupling means (10) of a tappet (1) for a valve train, which tappet (1)is installed in a bore (6) of a cylinder head (7) of an internalcombustion engine and can be switched to different valve lifts for atleast one gas exchange valve, said tappet (1) comprising an annular anda circular bottom section (2,3) arranged concentrically to each otherand contactable each one by a cam of different lift, the tappet (1)being guided in the bore (6) by a skirt (4) connected to the annularbottom section (2), said annular and circular bottom sections (2,3)being displaceable relative to each other and adapted to be coupled toeach other in the region of their common annular plane (8) by couplingmeans (10) which are displaceable radially by a servo medium at least ina first direction of displacement, the skirt (4) comprising at least oneinlet (25) for the servo medium, which inlet (25) serves to convey theservo medium from one end (22) of a supply gallery (23) which intersectsthe bore (6) of the cylinder head (7) to a reservoir (15) arranged in atleast one of the bottom sections (2,3) wherein a path (20) to the inlet(25) is created on or in the outer peripheral surface (5) of the skirt(4), an extent of the path (20) is such that the path (20) is inhydraulic communication with the end (22) of the supply gallery (23)during at least part of the stroke of the tappet (1), the method ofdisplacement of the coupling means in a further direction ofdisplacement by a mechanical spring means (11) comprising a first stepin which, prior to the further direction of displacement, the reservoir(15) is at least partly relieved of servo medium pressure during theentire time interval between a commencing valve lifting phase of the camand a subsequent base circle phase of the cam, and a further step inwhich, in the subsequent base circle phase of the cam, the reservoir(15) is completely relieved of the servo pressure required fordisplacement.